Most recreational divers practice No-Stop Decompression diving. The No-Stop Decompression Limits represent the depths and maximum times divers can stay on the bottom and then surface. All recreational dive tables assume that divers will not exceed recommended ascent rates.

Recommended ascent rates vary between 20 and 60 feet per minute. Although it is generally acknowledged that ascent rates may significantly affect dive safety, there is not enough human data to suggest the correct rate.

The goal of the Ascent Rate Study was to provide data to describe the effects of ascent rate.

Methods

Experiments were conducted in the hyper/hypobaric chambers at the Center for Hyperbaric Medicine and Environmental Physiology at Duke University Medical Center. All the dives were to 100 feet of seawater (fsw). The first profile had a bottom time of 15 minutes. When researchers accepted the dive profile, they increased the bottom time by three minutes. The tests involved single dives only.

Researchers tested ascent rates of 10 and 60 feet per minute. The objective of the study was to estimate if there is any difference in No-Decompression Limits, incidence of vascular bubbles, or decompression sickness between the ascent rates. Researchers accepted or rejected dive profiles based upon the number of DCS incidents and total exposures. They chose the acceptance and rejection rules to minimize the total number of DCS incidents, allowing for some mild cases but limiting more serious DCS. The Institutional Review Board of Duke University Medical Center approved these rules.

Subjects were dry and at rest throughout the dives. Subjects must have been certified recreational divers or have hyperbaric experience, be at least 18 years old, and their body composition must no exceed 40% of their ideal weight. Subjects could participate only once in each profile. Subjects were eligible for more than one study as the profile changes and they were encouraged to participate in each ascent rate profile. They under went a medical history review and a physical examination the day of the study by a DAN/Duke dive physician.

During the study, participantsí activity before, during, and after the 100 fsw dives were controlled and minimized. Except for essential activities such as medical examinations, clothing changes, Doppler monitoring, or trips to the bathroom, subjects remained seated for one hour before the dive and two hours after the dive. Climbing or descending stairs was strictly avoided for two hours before and three hours after diving. Subjects were compensated and participation was voluntary.